Inhibitors
Inhibitors occur when the immune systems of people being treated with blood clotting agents, such as nonacog alfan, start to regard the clotting agents as foreign objects.
The immune system will start to create proteins called antibodies to block the affects of the clotting agent. These antibodies are known as inhibitors.
The inhibitors can make medication used to treat haemophilia less effective. This means it is more difficult to prevent and control the symptoms of bleeding.
An estimated 20–30% of people who have treatment for haemophilia A develop inhibitors. Around 1–3% of people who have treatment for haemophilia B develop inhibitors.
Management of inhibitors
Immune tolerance therapy (ITT)
People with moderate to severe inhibitors are usually advised to try a treatment programme called immune tolerance therapy (ITT) to overcome them.
ITT involves receiving daily injections of either octocog alfa (for haemophilia A) or nonacog alfan (for haemophilia B). Over time, the immune system should begin to recognise the blood clotting agents and stop producing inhibitors.
ITT needs to be carried out on a long-term basis. Most people require a course of treatment that lasts 6–24 months. ITT is successful in an estimated 80% of cases.
Managing a bleed with inhibitors
In people with inhibitors, the original clotting agents do not work because they are removed from the body by the inhibitors. In the event of a bleed, a "bypass agent" must be used.
A bypass agent is a separate product that can be used to stop bleeding when inhibitors are still present. ITT doesn't work in some people and they need to use bypass agents for the rest of their life.
This may cause joint damage over time because bypass agents can only be used as needed, not as preventative treatment.
Joint damage
Joint damage can sometimes occur if haemophilia is poorly controlled. Successive joint bleeds can damage cartilage (the soft spongy tissue in joints that acts as a shock absorber) as well as the synovium (a thin layer of tissue that lines the inside of the joint).
Joint damage can often develop as a "vicious circle". The more damaged a joint is, the more vulnerable it is to internal bleeding. This in turn means that the joint will become even more damaged and vulnerable to bleeding.
Joint damage is more common in older adults who have severe haemophilia. This is because modern preventative treatments were not available in the past. It's hoped that modern treatments mean that children growing up today with haemophilia will not have joint damage.
Surgery can be used to treat joint damage. The procedure involves removing the damaged synovium to allow new synovium to grow in its place. If a joint is very seriously damaged, it may be necessary to replace the whole joint with an artificial one, such as a hip replacement or knee replacement.
